The invention relates to a radiant heating system having a high infrared heating capacity for processing chambers.
Such radiant heating systems are employed for example inside of processing chambers, e.g. vacuum chambers, in order to generate a requisite working temperature in a given space. Such temperatures may easily reach 3000° C. in the emitter region, and in the case of spaces of great area, an “array” having a plurality of emitters may alternatively be used, in order to achieve a uniform working temperature over a larger space.
Such radiant heating systems, however, have been found to have some disadvantages, considerably limiting their application. First, there is the problem that, especially in vacuum applications, electrical breakdown may occur at high operating voltages. This hazard arises especially during the process of evacuation. Second, especially high working temperatures and/or radiation outputs may be unattainable in a vacuum due to lack of adequate cooling of the infrared emitters.
To avoid breakdowns, the voltage may of course be reduced, but then the requisite radiation output cannot be attained. Besides, there is the possibility that the heating of the vacuum chamber may be cut off during evacuation. But this necessarily leads to an undesirable increase, or prolongation, of processing time.
U.S. Pat. No. 5,551,670 describes a high-intensity infrared heating device in which the lifetime of the infrared emitters is to be enhanced thereby. To accomplish this, each infrared emitter is arranged in a transparent quartz tube through which cooling air can be passed. For this purpose, copper are provided extending through the electrical connection contacts of the infrared emitter. In order not to affect the efficiency of the infrared emitters adversely, the surrounding air is passed into the quartz tube only at temperatures above 1500° F. (793° C.).
Further, EP-A-0,848,575 discloses a heating device having an array of tungsten-halogen emitters, in each instance ranged in a concentric arrangement of quartz, silicon or sapphire tubes. To concentrate the radiation generated and orient it in a preferred direction, one of the tubes is provided with a reflector in the form of a gold coating partly surrounding the tube.
Finally, U.S. Pat. No. 5,196,674 describes a furnace with protection for a heating element arranged in a quartz tube. The protection here provided against contact consists in a multiply slitted U-shaped housing of sheet metal enclosing the quartz tube with clearance.